Dissolving cellulosic esters



Patented June 10, 1947 DISSOLVING CELLULOSIC ESTERS John D. McCaleb, Baltimore, and Joseph J. Reis, Jr., Catonsville, Md., assignors to Pittsburgh Plate Glass Company, a corporation of Pennsylvania No Drawing. Application December 22, 1944, Serial No. 569,420

2 Claims. 1

The present invention. relates to a method of treating cellulosic esters such as cellulose triacetate for purposes of improving the solubility characteristics thereof in solvents and it has particular relation to the provision of a method of treating such esters in order to increase the solubility thereof in such solvents as mixtures of methylene chloride (dichloro methane) and minor amounts of methyl alcohol.

In the preparation of solutions of cellulosic esters and particularly of cellulose triacetate or cellulosic esters containing substantial amounts of cellulose triacetate, some difficulty is experienced in obtaining rapid and complete solution of the ester to provide a smooth and uniform solution. For example, it has been observed that when cellulose triacetate is treated with a solvent such as a mixture of 94 percent methylene chloride and 6 percent of methyl alcohol of 99 percent concentration, that even after substantial periods of time. solution is not entirely complete and lumps or particles of imperfectly dissolved material are present.

In accordance with the provisions of the present invention, it has been discovered that if the cellulosic ester is subjected to baking at a temperature substantially above atmospheric for a time before application of the solvents, its characteristics are greatly improved, both with respect to rate of dissolving and the smoothness and uniformity of the ultimate solution.

In practicing the invention, the cellulose ester. such as cellulose triacetate, can be heat-treated in a conventional drying oven or any other suitable heating apparatus. The temperature of heat treatment should be substantially above atmospheric but, of course, should not be so high as to induce appreciable decomposition or degeneration of the cellulosic ester. A suitable temperature of operation is approximately within a range of 212 to 220 F. The time of heattreatment may vary substantially, although satisfactory results are obtained within a range of approximately one to two hours. It is, of course, contemplated that lower temperatures as well as higher temperatures of treatment could be employed and that the period of treatment could be extended substantially so long as the cellulose triacetate is not decomposed or discolored. Shorter periods of treatment likewise are contemplated. The cellulosic mixture after such treatment can be dissolved very rapidly and completely in conventional solvent systems such as a solvent mixture of dichloromethane and methyl alcohol at room temperatures (say 68 F). Ap-

2 plication of the solvent preferably follows immediately, or only shortly after conclusion of the baking operation. The plastic may even be treated with solvent while it is still warm. However, it may, also, be allowed to cool to room temperature before such application.

In order to demonstrate the effects of heat treatment of cellulose triacetate two identical 20 gram samples were prepared. One of these was subjected to baking at 220 F. in an electric drying oven for two hours. The second sample was subjected to no heat treatment whatever. The two samples were then emptied into identical 57 cc. quantities of a mixture of dichloromethane containing 6 cos. of methyl alcohol of 99 percent concentration. The solvent mixture was at a temperature of 68 F. The samples were then subjected to constant stirring until solution was complete. The results of the solvent tests are tabulated as follows:

Heated cellulose trz'acetate a Time to dissolve to a Sample clear solution Minutes Seconds 0 l5 0 14% O 16 0 l6 0 l5 Uuheated cellulose trzacetate Time to dissolve to sample N lumpy solution Minutes Seconds Average solution time after heating: 15% seconds. V Average solution time without heating: 2 minutes, 2 /5 seconds.

Of course, the solvent can be warmed to any temperature below the boiling point, if so desired. Exposure of the plastic to solvent vapors is contemplated. Plastic may be added to the solvent mixture, or the mixture may be poured over the plastic.

It is to be observed that in the tests, the rate of solution of the heat-treated cellulose triacetate is far higher than that of the unheat-treated material and thatthe final product is a uniform smooth solution, whereas the material subjected to solvent action Without heat-treatment is in a lumpy state. Obviously, where the quantities of material being treated are great, the difierences in the rates of solution and the uniformity of the product are of substantial importance.

It will be apparent to those skilled in the art that the .formsof the invention herein illustrated are merely by way of examples and that numerous modifications may be made therein without departure from the spirit of the inventionv or the scope of the appended claims.

We claim:

1. A process of forming a uniform and smooth solution of cellulose triacetate in a mixture of methyl alcohol and dichloromethane which is a good solvent for cellulose triacetate, which process comprises preliminarily baking the cellulose triacetate at a temperature of about 212 F. to 220 F. for a period of about 1 to 2 hours, then imwith the solvent mixture.

2, A process of forming a uniform and smooth solution of cellulose triacetate in a solvent mixture consisting of about 94% of ethylene dichloromethane and 6% of methyl alcohol, which process comprises baking the cellulose triacetate at a temperature of about 212 to 220 F. for a period of about 1 to 2 hours, then immediately incorporating the cellulose triacetate with the solvent mixture.

JOHN D. MCCALEB. JOSEPH J. REIS, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

